Selective Si₃N₄ etching becomes challenging as the number of stacks in three-dimensional Not AND (3D NAND) flash memory devices increases. To suppress changes in the thickness of SiO₂ layers in Si₃N₄/SiO₂ multi-stack structures, etching inhibitors should be added to H₃PO₄ solutions. Notably, carboxylic acids can be adsorbed on OH-terminated substances, such as SiO₂, by forming Si-O-C bonds. Therefore, carboxylic acids added to H₃PO₄ solutions can be adsorbed on SiO₂ surfaces, and passivation layers can be formed, suppressing SiO₂ etching. When a Si₃N₄/SiO₂ multi-stack structure is dipped in a H₃PO₄ solution, the Si₃N₄ layers are removed, and the SiO_xN_y surfaces on the SiO₂ layers are converted into SiO_x surfaces with positively charged oxygen vacancies. For aromatic carboxylic acids, C=O bonds in their carboxyl groups can be converted to C-O^-, causing electrostatic attraction between the C-O^- groups and oxygen vacancies on SiO_x surfaces. Consequently, aromatic carboxylic acids can be adsorbed on SiO_x surfaces via the electrostatic attraction and Si-O-C covalent bond formation, creating robust passivation layers and suppressing SiO₂ etching. However, aliphatic carboxylic acids form only Si-O-C bonds on SiO_x surfaces and hence cannot realize the same functions as their aromatic counterparts.